Handle non existing collection

[yangwao]

When I open
https://kodadot.xyz/rmrk/collection/10352274-409E451AFD98397563-AURA3D-AURA-V-0000000000000006

Keeps loading, but users really don't know if it's an issue in internet, our bug or what's happening.

We should handle somehow that user is opening non-existing collection, item, etc.

[prachi00]

maybe we can handle this by routing the user to /collection if the collection doesn't exist? @yangwao